Maybe the problem is that Green Beret are WAY too powerful. Vision wins the war. I don't know why I would ever park a 4000pp unit in a base to create a crappy infantry unit when I could just use my GBs in the field and see everything coming and whack them with arty and cobras before they're even a problem. Maybe the VC need a guerrilla unit like the GB that can't be spotted easily and can impact significant destruction (maybe more mines, base or unit sabotage, stealthily affect village loyalty).
All this said, there are some strategic units in the game that I don't really see as relevant in the current game design, Armor, Mech Infantry and ARVN. It could be argued that wheeled warfare wasn't significantly relevant in the jungles of Vietnam anyway so why make them relevant in the game, but they're in the game and they really don't have much of a game play use. Not really sure how to affect air units or infantry in a way that would make wheeled warfare more relevant or if that is necessary. Maybe more threat to air cav, significant bonuses to wheeled units on roads?
ARVN are just pointless. They tie up the most important unit in the game to make a nearly useless unit. A couple well places GBs and the game is over. Not sure how to tone down GBs to make ARVN more a strategic necessity (disposable scouts vs the high value GB units). Currently GBs have almost zero threats in the game, that is a problem.
EDIT: OH! And the achievement that reduces the cooldown of air strikes is BACKWARDS! If I can get that achievement I need it HARDER not EASIER! Give me strategic advantages only if you're going to give me a more difficult level
